1. Field of the Invention
The present invention relates generally to a camera module for use in a mobile device. More particularly, the present invention relates to a hand-shake correction method and apparatus for correcting a shake of an image due to occurrence of hands shaking/trembling while holding a camera module during photographing.
2. Description of the Related Art
A conventional camera can provide shake-free high-resolution pictures at a shutter speed of 1/125 second or below, even though the hands of the user tremble somewhat during photographing of images. However, a camera mounted on a mobile device has a reduced quantity of light than the conventional camera during the photographing of images, because the lens aperture is smaller than that of the conventional camera, leaving less of an opportunity for ambient light to be received by the camera aperture. Therefore, the camera mounted on a mobile device uses a slower shutter speed to compensate for the lack of light, and when the camera in a mobile device photographs still images, an image shake may occur, thereby causing a blurred image, even when the degree of hand-shaking is slight due to the slow shutter speed, making it difficult to get the clear pictures. In particular, the problem of image shake due to the shaking hands is more considerable when the amount of ambient less is further reduced, such as in the low-light quantity indoor environment, at night time, or during a cloudy day. In addition, the image shake caused by the shaking hands is considerable even when the focal distance increases due to the use of a zoom function. During the photographing of not only still images but also moving images, a shake of the camera due to the shaking hands of a photographer who is walking or in a moving vehicle causes significant amounts of image blurring.
In order to solve the image-instability problem caused by the hand-shake and/or the shake of the camera-mounted device, there has been a long-felt need in the art for a technique of correcting the image-instability problems cause by shaking hands, and various hand-shake correction schemes have been developed to meet the need. Attempts at addressing this long-felt need include providing apparatuses that correct for the effects of shaking hands during photographing which are generally roughly divided into motion detector and a motion corrector.
With regard to a motion detector, a technique of measuring the motion of a camera-mounted device using a gyro sensor and a technique of detecting a motion of an image in a vector component by image signal processing have been proposed.
With regard to a motion corrector, which uses the motion information detected by the motion detector, the motion corrector corrects images in an optical or electronic manner. The known optical image correction schemes can be classified into a technique of refracting the incident light in an arbitrary direction using an angular-adjustable lens (or active prism), and a technique of returning an image deviated from the optical axis back to its original position by up/down/left/right-shifting a lens or an image sensor such as a Charge Coupled Device (CCD) and a Complementary Metal-Oxide Semiconductor (CMOS), using a piezo-electric device or a Voice Coil Motor (VCM).
The electronic image correction schemes can be generally classified into a technique of controlling an input position of a sensor, and a technique of storing image data in a memory and then controlling an address from which it reads the image data. Typically, the electronic image correction scheme has become popular for use in low-priced camcorders because it is suitable to correct moving images. On the other hand, the optical image correction scheme has become popular for use in high-grade camcorders and cameras because it is capable to correct both moving images and still images.
A method of shifting at least one of a lens, a CCD, or a CMOS image sensor by using a VCM is disclosed in Japanese Patent laid-Open No. 1999-007051, entitled ‘Lens Shift Device’, invented by Toyoda Yasuhiro, filed on 16 Jun. 1997 by CANON INC, and assigned an application No. 1997-172760.
In manufacturing a camera module for use in a portable mobile device, the size, weight and power consumption are particularly important factors that must be taken into consideration as portability and power consumption, particularly of a mobile terminal or telephone, are significant factors taken into consideration by the purchasers of such devices.
Therefore, consideration regarding size, weight, and power consumption is needed even in designing a hand-shake correction apparatus. Given that power consumption needed for operating an actuator including a lens or image sensor, which has a significant role in a hand-shake correction apparatus, increases with a size and weight of the actuator, there is a need in the art to provide an actuator and a controller that are smaller in size than the conventional components, including the lens or image sensor. Therefore, it is preferable that the hand-shake correction apparatus is modularized in a small size when manufacturing various sensors and other devices. The aforementioned consideration has particular applicability to the future development direction of state of the art mobile devices, in which a mobile phone, an MPEG Audio Layer-3 (MP3), a Portable Multimedia Player (PMP), a digital camera, etc. come out as all-in-one products including multiple functions.
Furthermore, when a conventional hand-shake correction apparatuses are actually miniaturized and implemented for use in mobile devices, the following problems may occur:
First, in realizing a function of measuring a hand-shake from a signal measured by a gyro sensor, errors between an actual signal value and a processed signal value may be accumulated due to offset, drift and phase delay.
Second, a VCM actuator can hardly expect its optimal control performance with the generally used controller, because it has a nonlinear characteristic, a time-varying characteristic in which its dynamic characteristic varies with the passage of time, and a hysteresis characteristic. The actuator including a lens or image sensor may suffer an actuation error that its actuation range decreases step by step due to the friction occurring between surfaces that contact each other during the actuation, even though it has issued an iterative command. Therefore, for the optimal control, there is a need for a controller improved from the existing Proportional Integrate Derivative (PID) controller which has been widely used in configuring a controller. In addition, it should be considered that even though the proposed controller is superior in performance, if there is excessive calculation, its implementation is not easy with the device such as an 8-bit processor generally used for control of miniaturized devices.
Third, because a correction pattern is variable according to users and circumstances, it is not possible to predict a control value for correction, so all calculations should be performed in real time within a very short time.